A known discharge lamp socket includes a starter transformer, a board on which capacitors and a spark gap are mounted, and a cover in which the starter transformer and the board are accommodated (see, e.g., Japanese Patent Document No. 2005-285368 A). The starter transformer includes a ferrite core, a secondary winding wound around the ferrite core, a sealing portion surrounding the secondary winding, and a primary winding wound around the sealing portion. A socket portion and the sealing portion are formed in a one-piece structure formed by resin molding. The socket portion includes an outer cylindrical portion inside which an outer circumferential surface of a base of the discharge lamp is fitted and an inner cylindrical portion that engage a circular recess at the bottom of the base. An inner electrode is coupled to a high-voltage end of the secondary winding, is exposed at the socket portion, and is surrounded by the outer cylindrical portion of the socket portion. Further, in order to prevent an electric discharge between the inner electrode and electronic parts, such as the capacitors and the spark gap inside the cover, the ferrite core, the secondary winding, and a coupling portion between the secondary winding and the inner electrode is sealed inside the resin molded structure.
However, the resin molding requires special equipment to prevent, for example, blowholes in the resin. Also, the manufacturing process is complicated. Further, in the event that a crack is generated in a rigid portion of the resin due to a temperature variation or aging degradation, an electrical insulation failure may result, making it difficult to maintain stable lighting of the lamp. Furthermore, the resin molded structure increases the weight of the socket itself, which is disadvantageous in that the optical axis of the discharge lamp is likely to deviate from proper alignment due to vibration of the vehicle.